Method of producing lead bead bearing steel

ABSTRACT

METHOD FOR PRODUCING LEAD-BEARING STEEL AND THE PRODUCT PRODUCED THEREBY COMPRISING DISCHARGING A STREAM OF MOLTEN STEEL FROM A MELTING FURNACE TO A LADLE, AND ADDING LEAD TO THE STREAM OF MOLTEN STEEL AS IT IS BEING DISCHARGED FROM THE MELTING FURNACE AT TEMPERATUREA ABOVE 1600*C. AND CONTROLLING THE TEMPERATURE OF THE BATH, AND DISSOLVING OXYGEN IN THE BATH IN THE LADLE IN ORDER TO FAVOR THE FORMATION OF LEAD-OXIDE.

p 4, 19-73 J. J. A. ORMAECHEA 3,756,805

METHOD OF PRODUCING LEAD-BEARING STEEL Filed Oct. 9, 1970 3 Sheets-Sheet1 Sept. 4, 1973 J. J. A. ORMAECHEA 3,756,805

METHOD OF PRODUCING LEAD-BEARING STEEL 5 Sheets-Sheet 2 Filed Oct. 9,1970 p 1973 J. J. A. ORMAECHEA 3,756,805

METHOD OF PRODUCING LEAD-BEARING STEEL I5 SheetsSheet 3 Filed Oct. 9,1970 United States Patent Oihce 3,756,805 Patented Sept. 4, 19733,756,805 METHOD OF PRODUCING LEAD-BEARING STEEL Jose Joaquin AguirreOrmaechea, Independencia 1,

Vitoria, Spain 7 Filed Oct. 9, 1970, Ser. No. 79,529 Claims priority,applgisatiosrg Spain, Feb. 3, 1970,

Int. or. can 39/54 US. (:1. 75 -58 5 Claims The present inventionrelates to an improved method of making steel and a product producedthereby.

The present invention. relates particularly to the manufacture oflead-bearing steels, having a lead content of between 0.10 and 0.8%which is distributed finely and homogeneously throughout the entire massof the steel.

As is well known, lead-bearing steels have a greater machinability, whenworked on chip-producing machinetools, than steels of the same basiccomposition that do not contain lead.

- can also be observed in a magnetoscope test for magnetic ,Knownclassical methods of producing lead-bearing steels are based upon thehiterto accepted supposition that lead is insoluble in steel. a

In order to produce, by classical methods, lead-bearing steels having anadequatedegree of homogeneity, it has been thought necessary to add thelead in the form of granules, just before the steel solidifies, with theobject of avoiding segregation of the lead due to gravity and -'-as aresult of the substantial difference between the density of steel and oflead Consequently, in the classical meth- 0d, the granules of lead areadded to the molten material .at the moment atwhich it is poured intothe mold.

Contrary to the method of the present invention, the classicalmethodsrequire precise co-ordination of. the stream of granules and the streamof molten steel at the moment when addition takes place, and this callsfor very great care as well as a high degree of professional skill onthe part of the personnel in charge of the process of manufacture. I 1

Nevertheless, the principal drawback to the methods hithertoused-resides in the fact that, with these methods,

it is not possible to produce steels in which the lead is distributed inahomogeneous manner. This segregation of "lead of varying intensityalways occurs, as well' as agglomerations of this element, which breakup the metallic structure and lower the quality of the steel.

The absence of homogeneity and the existence of segregations can berevealed by theWragge impression or particles, and by microscopicexamination.

Because the above-mentioned deficiencies, steel manufactured by theclassical methods have generally been used for the production of partssubjected to low or medium load when in service. 1

It is an object of the present invention to provide a method of makinglead-bearing steel, avoiding the abovementioned disadvantages, and inwhich solid or liquid lead is added to a stream of molten steel as it isdischarged from a melting furnace to a ladle. With this and otherobjects in view which will become apparent from the following detaileddescription, the present invention will be clearly understood inconnection with the accompanying drawings in which:

FIG. 1 is a schematic vertical longitudinal section through a meltingfurnace, a ladle and the means for adding the lead at the moment atwhich the metal is poured into the ladle and the addition of lead ismade;

FIG. 2 is a schematic vertical longitudinal section through the ladleshowing one construction thereof according to the present invention ofthe ladle outlet; and

FIG. 3 is a schematic vertical longitudinal section through the ladleshowing another ladle outlet construc tion.

Referring now to the drawings, and more particularly to FIG. 1, there isshown a melting furnace 1, from which a stream of molten steel 2 passesfrom the melting furnace 1 to a ladle 3. A feed means 4 feeds a solid orliquid lead into a duct 5 which carries the lead to the molten stream ofmetal with which it joins up at point 6.

The ladle outlet 7 is more particularly disclosed in FIGS. 2 and 3QFIG.2 shows an arrangement in which a base 8 of the ladle has a projectingportion orupstanding rim9, whereby it israised above the openingofitheladle outlet. In FIG. 3 there is shownianotherarrangement in whicha sleeve 7 defining the ladle outlethas one end thereof raised abovetheflatnbase 8 of the ladle. A plug 10 is providedforopening and closingthe'ladle outlet:

cient to permit theformation of lead-oxide, the vapour of which issolublein the molten steel. The lead-oxide formed has a low boilingpoint and causes bubbling of the steel bath which becomes saturated withthis compound.

The bubbling caused by the lead-oxide" vapour which passesthrough thebath and saturates it, reduces the cori- 'tent of oxygen, hydrogen andother gases dissolved inthe steel, and thus indirectlyimproves thequality of'the 'steel.

The amount of reactive oxygen necessary for the formation of lead-oxidewilldepend upon the composition of the steel, and'care is taken" not toadd aluminium to the bath before the lead has been added. e

In the case of aluminium-killed "steelsfalumitiium 'is added to themetal in-the ladle in the finatst ages. This constitutes no drawbacksince it corresponds to normal manufacturing procedure.

Table No. 1 shows the solubility of lead-oxide as a function of thetemperature of the bath, as established on the basis of numerous tests:

TABLE NO. 1

Percent Pb dissolved in the form of PbO Temperature of the bath indegrees C.:

The solubility of lead in steel is independent of the composition of thesteel and is determined solely by temperature.

The temperature at which the metal is poured into the ladle should begreater than 1600 C. and is governed by the percentage of lead requiredin the steel, as shown in Table No. 1.

As can be seen from the table, when the temperature of the bath dropsbelow 1600 C., as occurs in most cases when the steel is still in theladle, the solubility of the lead in the steel is practically zero.Under these conditions lead-oxide is precipitated in the form of a fineand homogeneous dispersion, the particles of which do not settle bymeans of gravity, so that the lead is homogeneously distributed aftersolidification has taken place.

The remainder of the lead, insoluble in the steel at the temperature atwhich the addition is made, forms relatively large droplets, which eachsettle by gravity over a period of time not greater than 5 minutes, andare deposited on the base of the ladle. Thus, after the lead has beenadded, a minimum period of about 5 minutes should be allowed to elapseso that this deposition can take place before the steel is poured intothe mold.

The quantity of lead added in solid or liquid form should be greaterthan that theoretically required, and preferably should be 40% greaterthan the quantity that it is desired to incorporate in the steel.

The lead is added at the feed point via means 4 (FIG. 1) at a rate equalto that required at the upper part 6 of the stream of molten steel.

The rate of supply of the lead needed at the feed point 4 in FIG. 1 canbe determined by simple tests, the aim being to have a supply of solidor liquid lead reaching the stream of molten metal during practicallythe entire period during which pouring takes place. Nevertheless, thesystem does not call for a high degree of co-ordination in thisoperation, since, as previously indicated, if too much lead is addedthis does not become incorporated in the bath but is deposited on thebase of the ladle.

The method of the present invention does not require any high capitalcost equipment. The only requirement is that of positioning the ladleoutlet 7 or a rim 9 in such a way that it projects upward of or beyondthe plane of the base 8 of the ladle 3, thus preventing the lead,deposited on the base, from being entrained by the stream of steel whichemerges through the mouth-piece 7 when casting takes place.

Despite the above-mentioned precautions, a small quantity of lead may bedeposited directly on the surface of the ladle outlet. This lead can beeliminated simply by slight purging of the steel prior to casting it inthe mold.

The method to which the present invention relates can be applied to allkinds of steel compositions and can be adopted in present-daysteel-producing techniques.

The method of the present invention can be used in all the usualsteel-making processes, for example, Siemens- Martin, electric furnace,L.D., continuous casting, or mold-casting by the siphon or directmethods.

These improvements result in advantages regarding an even andfinely-dispersed distribution of the lead both at the top and the bottomof the ingot. Similarly, segregations do not occur either on the surfaceor in the middle of the ingot.

Consequently, ingots manufactured by the method of the present inventiondo not need to be end-cropped, as is the case with ingots manufacturedby the classical methods.

In this connection, experience from numerous casting operations hasshown that with the method of the present invention, an output can beobtained that is of the same order of magnitude as that obtained withsteels of an identical basic compositions, but containing no lead.

The lead particles form a fine, homogeneous dispersion, the grain-sizeof which is often less than one micron.

Tests carried out so far using the new method in accordance with thepresent invention show that this particular method for the addition oflead has no adverse effect upon the fatigue behaviour of the steel orupon its mechanical properties.

While I have disclosed one example of the present invention, it is to beunderstood that this example is given by illustration only and not in alimiting sense.

I claim:

1. A method of producing lead-bearing steel, containing a uniformdistribution of lead, comprising the steps of discharging a stream ofmolten steel from a melting furnace into a ladle,

adding lead to said stream of molten steel at the moment as it is beingdischarged from said melting furnace between the latter and the ladle attemperatures above 1600 C. and controlling the temperature of the bath,and

dissolving oxygen in the bath in the ladle in order to favor theformation of lead-oxide.

2. The method, as set forth in claim 1, wherein sufficient lead is addedto said stream of molten steel to provide a lead content of 0.10 to0.80% by weight homogeneously distributed in said steel.

3. The method, as set forth in claim 1, further comprising the step ofallowing the steel in said ladle to stand for at least 5 minutes beforeit is poured or tapped into a mold.

4. The method, as set forth in claim 3, further comprising the step ofaluminium-killing said steel after it has been allowed to stand for atleast 5 minutes and before it is poured or tapped.

5. The method, as set forth in claim 1, further comprising the step ofpreventing any deposited lead from being discharged from said ladle bycatching said deposited lead in a projecting rim adjacent the dischargeof the ladle.

FOREIGN PATENTS 4/ 1940 Great Britain -123 F L. DEWAYNE RUTLEDGE,Primary Examiner U.S. Cl. X.R.

